Reflection properties of metallic gratings on ZnO films over GaAs substrates

A potential application for piezoelectric film deposited on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Metallic gratings are basic elements-required for the construction of such devices, and analyzing the reflectivity and the velocity change due to metallic gratings is often a critical design parameter. In this article, the Datta and Hunsinger technique is extended to the case of a multilayered structure, and the developed technique is applied to analyze shorted and open gratings on ZnO films sputtered over (001)-cut (110)-propagating GaAs substrates. The analysis shows that zero reflectivity of shorted gratings can be obtained by a combination of the ZnO film and the metal thickness and the metallization ratio of the grating. Experiments are performed on shorted and on open gratings (with the center frequency of about 180 MHz) for three different metal thicknesses over ZnO films which are 0.8 μm and 1.6 μm thick. From the experiments, zero reflectivity at the resonant frequency of the grating is observed for a reasonable thickness (h/λ=0.5%) of aluminum metallization. The velocity shift between the shorted and the open grating is also measured to be 0.18 MHz and 0.25 MHz for 0.8 μm and 1.6 μm thickness of the ZnO film, respectively. The measured data show relatively good agreement with theoretical predictions